This invention relates to a raster-scanned cathode ray tube display with a cross-hair cursor and more particularly to a multiple line cross-hair cursor.
Raster-scanned cathode ray tubes having bit-per-pel refresh buffers or mapped memories are well known in the art. Also known in the art are cross-hair cursors which allow an operator to interact with the CRT screen using either a keyboard or a graphics attachment such as a "mouse" to move the cursor around the screen.
Operator productivity and usability of the display are enhanced by employing a two or three line cross-hair cursor, i.e., a cursor formed with two or three horizontal lines and two or three vertical lines, with the intersection of the central lines of the three line cursor indicating the point of interest. Such a cursor can be made more legible than the normal single-line cross-hair cursor by controlling the display modes of the different lines. Thus, by making the central line of a three line cursor invisible--in effect displaying a hollow cross--the point of interest at the intersection will not be obscured when the cursor is positioned over it. In other instances, it may be desirable to allow an operator to select the cursor to display each line in a different color or intensity so that the cursor will always contrast with the background whatever the color or intensity of the latter.
To avoid the need to rewrite the bit buffer every time the cursor is moved, it is preferred that the cursor defining bits should be generated and mixed with the bit pattern outside the buffer.
For front-of-screen performance reasons, conventional cathode ray tube displays use interlaced scan lines so that "odd" and "even" fields are interleaved to form a frame. A problem arises with an interlaced display using a two or three line cursor, since the different lines of the cursor will be displayed on different fields. The present invention provides a solution to this problem and allows control of the cursor with a minimum of logic. In addition, use of a 2 or 3-line cursor provides a steadier, less flickery cursor than a single pel cursor on an interlaced display, since at least one line of the cursor can be refreshed at each field, whereas the single line cursor can only be refreshed every other field.